1. Field of the Invention
This invention relates to an antiglare film to be provided on the surface of windows, displays and the like. In particular, the invention relates to an antiglare film to be provided on the surface of a display such as a liquid crystal display (LCD), a CRT display, an organic electroluminescence display (ELD), a plasma display (PDP), a surface-conduction electron-emitter display (SED), and a field-emission display (FED).
2. Description of the Related Art
In a display such as a liquid crystal display, a CRT display, an EL display and a plasma display, in order to prevent a reduction in visibility caused by outside light shining onto the surface of the display during viewing and listening, it is known to provide an antiglare film having a rugged structure on the surface of the display.
For antiglare films, for example, the following techniques are known:
a technique in which a rugged structure is formed on the surface of an antiglare film by an embossing method; and
a technique in which a rugged structure is formed on the surface of an antiglare film by coating a coating liquid prepared by mixing particles in a binder matrix-forming material to disperse the particles in the binder matrix.
In the antiglare film having a surface with a rugged structure, because of the scattering of the outside light incident on the antiglare film by the rugged structure on the film surface, the image of the outside light becomes unclear, thereby making it possible to prevent a reduction of visibility caused by shining of outside light onto the display surface.
Here, for an antiglare film with irregularity formed by embossing on the surface, the surface irregularity can be controlled completely. Therefore, reproducibility is good. However, there is a problem that, if there is a defect or a foreign material on an embossing roller, endlessly repeating defects will appear on the surface at the pitch of the roller.
On the other hand, antiglare films using a binder matrix and particles are produced with a smaller processing number than that for antiglare films using the above-described embossing. Therefore, it can be produced at a low cost. Thus, many forms of antiglare films prepared by dispersing particles in a binder matrix are known (JP-A-6-18706).
For antiglare films using a binder matrix and particles, various techniques have been disclosed, including, for example, the following techniques:
a technique in which a binder matrix resin and the combination of spherical particles and indefinite-form particles are used together (JP-A-2003-260748);
a technique in which a binder matrix resin and plural types of particles having different particle sizes are used (JP-A-2004-004777);
a technique in which surface irregularity is employed, wherein the cross-section area of the concave portion is defined (JP-A-2003-004903).
Further, the following techniques are also disclosed:
a technique in which the combination of internal scattering and surface scattering is employed to give an antiglare layer having internal haze (cloudiness) of 1-15% and surface haze (cloudiness) of 7-30% (JP-A-11-305010);
a technique in which a binder resin and particles having particle diameters of from 0.5 to 5 μm are employed, wherein the difference between the refraction index of the resin and that of the particle is determined to be from 0.02 to 0.2 (JP-A-11-326608);
a technique in which a binder resin and particles having particle diameters of from 1 to 5 μm are employed, wherein the difference between the refraction index of the resin and that of the particle is determined to be from 0.05 to 0.15. In addition, a solvent to be used, surface roughness and the like are determined to be within a certain range (JP-A-2000-338310);
a binder resin and plural types of particles are employed, wherein the difference between the refraction index of the resin and that of the particle is determined to be from 0.03 to 0.2 (JP-A-2000-180611); and
a technique in which, for the purpose of lowering the reduction in contrast, change of hue and the like upon changing a viewing angle, the surface haze (cloudiness) is determined to be 3 or higher, and the difference between the haze value in the normal direction and the haze value in ±60° directions is determined to be 4 or lower (JP-A-11-160505).
As described above, there are disclosed antiglare films having various structures for various purposes.
The performance of an antiglare film used for the front of a display varies depending on situations and displays. In other words, the optimum antiglare film varies depending on the resolution and intended use of a display. Accordingly, a variety of antiglare films are required in accordance with intended uses.
Regarding displays used for a monitor of notebook computers or desktop personal computers, users often watch a display screen from the front direction for a long period of time. Therefore, for an antiglare film used for a monitor display of notebook computers or desktop personal computers, such antiglare films are required that (1) they have high antiglare property capable of making images of outside light, which is incident on the surface of a display in the perpendicular direction (that is, in the front direction to the display screen), unclear, to prevent the shining of an image of the outside light, and (2) they are not accompanied with such phenomenon as fading (white blurring) upon the incidence of outside light, in particular illuminating light from a fluorescent lamp etc., onto the display surface.